Silicone catheter and process for manufacturing same

ABSTRACT

An improved catheter comprising a tubular body portion comprising a primary lumen and an inflation lumen and an outer covering, a portion of which is inflatable to form an anchoring bubble, wherein a layer of thermoplastic material is applied around the tubular catheter body in the region underlying the anchoring bubble, the thermoplastic layer containing a hole through which an inflation medium can be injected from the inflation lumen to expand a portion of the outer covering to form the anchoring bubble and the thermoplastic layer being composed of a material to which the outer covering does not adhere.

[ 1 Dec. 16, 1975 SILICONE CATHETER AND PROCESS FOR MANUFACTURING SAME[75] Inventor: Donald A. Todd, Elk Grove Village,

[73] Assignee: Western Acadia, Incorporated, Chicago, Ill.

[22] Filed: July 25, 1974 [21] Appl. No.: 491,623

[52] US. Cl 156/155; 128/349 B; 156/191;

156/253; 156/289 [51] Int. Cl. B65H 81/00 [58] Field of Search 156/191,155, 250, 251,

156/252, 261, 263, 293, 294, 108, 289; 128/349 B, 349 R; 264/316-317,221, DIG. 44, 163, 154; 117/4, 6, 8', 83/16 Clark et a1 156/155 X Schaar117/4 X 3,292,627 12/1966 Haravtuneian 128/349 13 3,734,100 5/1973Walker et a1 128/349 B x FOREIGN PATENTS OR APPLICATIONS 1,234,0376/1971 United Kingdom 128/349 B Primary Examiner-Douglas J. DrummondAssistant Examiner-David A. Simmons Attorney, Agent, or Firm-Dennison,Dennison, Townshend & Meserole [57] ABSTRACT An improved cathetercomprising a tubular body portion comprising a primary lumen and aninflation lumen and an outer covering, a portion of which is inflatableto form an anchoring bubble, wherein a layer of thermoplastic materialis applied around the tubular catheter body in the region underlying theanchoring bubble, the thermoplastic layer containing a hole throughwhich an inflation medium can be injected from the inflation lumen toexpand a portion of the outer covering to form the anchoring bubble andthe thermoplastic layer being composed of a material to which the outercovering does not adhere.

9 Claims, 5 Drawing Figures .k Mill/[11111111111111 U.S. Patent Dec. 16,1975 AvN SILICONE CATHETER AND PROCESS FOR MANUFACTURING SAME BACKGROUNDThe present invention concerns improvements in the method formanufacturing a silicone catheter, a tubular medical device forinsertion into the body for the purpose of injecting or withdrawingfluids. Although the invention is described in the followingspecification with particular reference to a Foley catheter forinsertion in the urethra, the invention is equally applicable tosimilarly constructed medical devices such as endotracheal tubes,tracheal tubes, Dennis tubes (used for decompressing the intestinaltract prior to or after gastrointestinal surgery), rectal catheters,Trocar catheters, hematuria balloon catheters, heart catheters, andothers. In addition, the concepts of this invention could also beapplied to similarly constructed non-medical devices.

The typical Foley catheter consists of a tube or shaft containing aprimary lumen which is the conduit for removal or insertion of theappropriate fluid. Within this primary lumen and attached to the wallthereof is at least one secondary, smaller lumen which is the conduitfor the injection of an appropriate gas or fluid for inflation of aballoon anchoring the catheter inside the patient. The anchoring balloongenerally consists of a thin, elastic material extending around theexterior of the catheter near its tip and attached at its edges orshoulders to the exterior of the catheter. A hole in the tube wallpermits the inflation gas or fluid to enter underneath the elasticmaterial and expand it to a balloon-like configuration.

In use the catheter is inserted into the body cavity, and an inflationfluid is pumped through the secondary lumen to expand the anchoringballoon. This prevents accidental removal of the catheter from thepatient and stations the catheter in the appropriate position forefficient use. Once the catheter is so anchored, body fluids can bedrained or therapeutic fluids can be injected into the body through theprimary lumen. When the catheter is no longer needed, the inflationballoon is deflated by releasing the inflation fluid or gas and thecatheter is withdrawn from the body.

Although this basic design for a catheter has been used for a number ofyears, serious problems remain in the design and method of constructionof these devices. In particular, there are problems with the previousmethods which have been used to provide the elastic exterior portionwhich forms the anchoring bubble. For example, in US. Pat. No. 3,734,100issued to Walker et al. a catheter construction is described in which aseparate cuff portion is glued at its shoulders to the surface of thecatheter. Although the patent illustrates the exterior surface of thecatheter as being smooth and regular, unfortunately, in practice thethickness of the cuff portion and the effects of the glue cause surfaceirregularities at the cuffs shoulders. Thus, in a typical catheterproduced by the process of Walker et al. the shoulders of the cuff willprotrude beyond the remaining exterior surface of the catheter. Thissituation is undesirable because such irregularities impede theinsertion or withdrawal of the catheter and increase the discomfort tothe patient. In addition, such a catheter construction is generally notamenable to mechanized production, and manufacture of the catheters byhand causes additional imperfections and defects.

As an alternative, it has been suggested to cover the exterior of thecatheter tube in the area underlying the bubble with a masking (release)material, coating the tip of the catheter including the bubble regionwith a flexible, inflatable material, and subsequently removing theunderlying masking material. For example, in the patents to Harautuneian(US. Pat. No. 3,292,627 and 3,304,353) the use of a water solublemasking material is suggested. However, there are several problems withthis design. First, in simultaneously removing the water soluble releasematerial and inflating the anchoring bubble, difficulties in thedissolution of the release material frequently cause particles to becomelodged in the inflation lumen preventing further expansion of theanchoring bubble. Similarly, as discussed in Harautuneians US. Pat. No.3,452,756, the masking layer may only dissolve in the localized areaadjacent the hole to the inflation lumen. Thus, the anchoring bubble mayexpand preferentially in that area and cause localized pressureinjurious to the body tissue. The same general type of system is shownin British Pat. No. 1,234,037Steer et al.

Alternatively, US. Pat. No. 3,544,668 issued to Dereniuk illustrates theuse of a gel as a masking layer beneath the anchoring balloon. Followingthe formation of the outer skin on the catheter, the gel layer isvolatilized by heat. This method is difficult to practice because theouter covering of the catheter must be applied before the releasecoating has dried or is touched.

A further difficulty encountered with the prior art processes formanufacturing a catheter is that they are not applicable to the mostuseful catheter material, silicone. It has been found that silicone ismore compatible with human tissue than previously used rubber andplastic materials and that the incidence of infection in the bodytissues is appreciably reduced with silicone catheters. Althoughattempts have been made to apply silicone coatings over conventionalcatheter tube materials, silicone bonds poorly with the majority ofthese other materials. Accordingly, it is preferable to construct theentire catheter of silicone. Because of silicones hydrophobic nature,however, it is difficult to apply coatings such as those in theHarautuneian and Dereniuk patents to silicone. Thus, in addition to theproblems generally encountered with water soluble or volatile releasecoatings, a further defect is that these coatings are not useful inpreparing silicone catheters.

In view of the foregoing. it is an object of the present invention toprovide an improved catheter construction and a method for facilitatingthe construction of these catheters.

It is also an object of this invention to provide an improved siliconecatheter and a method for constructing catheters made entirely ofsilicone.

It is also an object of this invention to provide a method forconstructing catheters in a mechanized operation.

It is a further object of this invention to provide a catheter whichdoes not suffer the defects of localized swelling fo the anchoringbubble or the plugging of the inflation lumen caused by the particlesfrom the release coating.

SUMMARY OF THE INVENTION The invention comprises an improved catheterdesign and a method for constructing this catheter.

The catheter comprises atubular body comprising a larger primary lumenand a smaller inflation lumen; a smooth tip at the distal end of thecatheter body which seals the primary and inflation lumens; an outercovering enclosing the tubular catheter body and the tip; the tubularcatheter body containing a first hole to permit communication of fluidsthrough the outer covering between the exterior of the tube and theprimary lumen and a second hole permitting communication between theexterior of the tube and the inflation lumen but not through the outercovering; and a thin thermoplastic tape surrounding the tube underneaththe outer covering and overlapping the second hole, the width of thetape corresponding to the desired base of the anchoring bubble formed byinflation of a portion of the outer layer, the tape containing a holeadjacent said second hole to permit the inflation of the anchoringbubble and the tape comprising a mate rial to which said outer layerdoes not adhere.

The method comprises the steps of forming a tubular catheter bodycomprising a larger primary lumen and a smaller inflation lumen insidethe primary lumen, forming a first hole in the wall of the tubular bodyto permit communication between the inflation lumen and the exterior ofthe tube, forming'a smooth tip to the distal end of the tubular body,applying a thin layer of thermoplastic tape to the exterior of thetubular body underneath the portion of the outer layer which forms theanchoring bubble and overlapping the first hole, applying an outer layerof covering material which does not adhere to the thermoplastic tape tothe exterior of the tubular body to form a covered tube, forming asecond hole in the covered tube to permit communication between theprimary lumen and the exterior of the covered tube and forming a thirdhole in the thermoplastic tape adjacent the first hole.

DESCRIPTION OF THE DRAWINGS The invention is illustrated by thefollowing drawings in which FIG. 1 is a top view of the uninflatedcatheter.

FIG. 2 is a partially cutaway side view of the uninflated catheter.

FIG. 3 is a cross section of the uninflated catheter taken along line 3.

FIG. 4 is a cutaway side view of the catheter illustrating the inflatedanchoring bubble.

FIG. 5 is a cross section of the uninlfated catheter taken along line 4.

Referring to the drawings, the first step in the preparation of thecatheter is the formation of tube comprising primary lumen 12 andinflation lumen 14. The cross-sectional shape and orientation of thesetwo channels may take various forms other than that shown in FIGS. 3 and5. However, to provide the minimum amount of resistance for insertioninto the patient, it is desirable that the exterior cross section of thetube be essentially round. Formation of this tube can be accomplished byany ordinary procedure, such as extrusion, wherein a continuous lengthof tubing is formed. The tubing is then cut to the appropriate lengthdesired for the catheter.

After the tubular body of the catheter is formed, an inflation hole 18is formed in the exterior of the tube. to provide a passage to theinflation lumen. This hole is located at an appropriate distance fromthe distal end of the catheter tube where the anchoring bubble is to belocated. The distal end of the catheter refers to the end which isinserted into the patient. The hole can be formed by any standardprocedure, such as cutting or punching the exterior of the cathetertube.

Following the formation of the inflation hole a layer of thermoplasticmaterial 20 is wrapped around the tube so that it covers the inflationhole. An appropriate thermoplastic material is a thermoplastic tapewhose adhesive side adheres to the exterior of tube 10 but whoseopposite side does not adhere to the subsequently applied outer layer ofthe catheter. The wrapping of the thermoplastic tape can be accomplishedby hand or by mechanical means in such a manner that the ends of thetape overlap very slightly. This will insure that the outer coveringwhich forms the anchoring bubble will not adhere to any portion of theunderlying tube. In addition, the thermoplastic tape should be thin, forexample less than 0.05 inch and, preferably, approximately 0.004 inch inthickness. This should avoid any impairment to the insertion of thecatheter into the body caused by an enlargement of the outside diameterof the catheter tube in the region adjacent the thermoplastic tape.

Following the application of the thermoplastic tape a tip 16 is formedon the distal end of the catheter. Al-

though the tip shown in the drawing is semi-spherical in shape, theactual configuration of the tip can take any form which facilitates theinsertion of the catheter into the body. Preferably the tip is molded tothe tubular body, for example, by placing the end of the tube into anopen metal form filled with liquid material. This method of forming thetip is preferred, since it provides a secure seal of the inflation lumenat 22. Without such a seal it would be difficult, if not impossible, toinflate and maintain the anchoring bubble.

After these essential elements of the catheter are formed and assembled,an outer layer of material is applied over the length of the catheter bydipping the catheter into a solution of the covering material. Thecoating is dried and cured at room temperature and humidity over nightor more rapidly at elevated temperatures. Additional coatings may berequired to achieve the desired thickness of the outer layer. Theprocedures for dip coating a catheter with silicone are known to thoseskilled in the art as shown, for example, in US. Pat. No. 3,434,869,issuedto Davidson. As illustrated in the drawings, the completed coatedcatheter has a smooth outer surface which does not present anyprotrusions which might impede the insertion or extraction of thecatheter from the body.

Following the formation of the coating, hole 26 is punched in thecatheter wall to provide a channel between the primary lumen and theexterior of the catheter. Although this hole can take any shape andsize, as shown in the drawings, identical oval holes are punched onopposite sides of the catheter to facilitate injection or withdrawal offluids from the body.

Finally, an inflation hole 28 is formed in the thermoplastic tape. Thishole is adjacent the inflation hole 20 previously cut in the wall of thecatheter tube. The thermoplastic tape is pierced by touching thesilicone coating over the opening 18 with a hot probe the temperature ofwhich is adjusted to melt the thermoplastic tape but not to affect thesilicone outer coating.

The advantages of the present invention are readily apparent from FIG. 4which shows the anchoring bubble of the catheter in its inflatedposition. When the inflation fluid or gas is forced through inflationlumen 14, it inflates the bubble as shown in FIG. 4. Since the maskingmaterial does not have to be dissolved during inflation, the inflationoccurs steadily and uniformly and the inflation lumen will not becomeplugged by particles of partially dissolved masking material.

As mentioned previously, it is desirable to build the entire catheter ofsilicone because of its compatibility with human tissues. Typically thetubular catheter body and the tip are made of much harder silicones thanthat used for the outer covering.

The thermoplastic masking tape may be made of any thin material whoseadhesive side adheres to the tubular body of the catheter, whoseopposite side does not adhere to the outer coating of the catheter, andwhich melts at a temperature significantly lowerthan that of the outercoating. Where the tubular body and outer coating are both made fromsilicone, a suitable release material consists of unreinforcedpolyethylene or polypropylene tape having a thickness of approximately0.005 inch.

Typical properties of materials presently available which are suitablefor use in the present invention are designated in Table I.

Cured at elevated temperature and pressure in the presence of peroxide.

"Mixed with a catalyst, normally a metallic soap, and cured at roomtemperature "Cured by exposure to moist air at room temperature.

Following the formation of the catheter illustrated in the drawings itis also desirable to mold to the external end of the catheter suitableapparatus containing a provision for injecting gas or fluid into theinflation lumen and for connecting the primary lumen to suitabledrainage or injection means. A typical device is shown, for example, inUS. Pat. No. 3,769,981 to McWhorter et al.

EXAMPLE A silicone catheter was prepared according to the followingprocedure. First, a silicone mixture was prepared using the heat curedsilicone rubber described in Table II and 1.0 percent of a catalystcomprising bis 2-4 dichlorobenzoyl peroxide (Cadox TS-50). This mixturewas extruded into a tube comprising a primary lumen and an inflationlumen arranged as shown in FIGS. 1 through 5. This tube is extrudedthrough a tunnel maintained at about 900F and has a residence timewithin the tunnel of approximately l-4 minutes. As the tube leaves thetunnel it is cut to the size appropriate for the particular applicationof the catheter. Subsequently, a hole is punched at the distal end ofthe tubular body of the catheter at the location of the anchoringballoon, the hole providing a passage to th inflation lumen.

At this point the tip is formed on-the distal end of the catheter. Aliquid two-part silicone rubber (as described in Table II) is pouredinto a steel mold, and the distal end of the catheter is immediatelyinserted into the mold. The catheter is permitted to remain in the moldwhile the silicone tip is cured. The catheter is removed from the moldand cured for four hours at 350f. This process drives off any remainingcatalyst and completes the cure of the catheter body.

The catheter is prepared for dip coating by applying a strip ofpolypropylene tape around the catheter tube so that it overlaps thepreviously punched hole. The catheter is then dipped into a 40 percentsolvent solution one-part room temperature vulcanized silicone rubber(as described in Table II) and cyclohexane, withdrawn at a slow, steadyrate, inverted and dried for 40 minutes at 120F. This dipping and dryingprocedure is repeated two additional times. On the final (third) coatingblue dye is added to the silicone solution to add color to the catheter.

Following the final drying step, two elliptical drainage holes arepunched in the distal end of the catheter to provide communication ofthe drainage lumen with the exterior of the catheter. A probe heated to500F is then applied for about seconds to the catheter skin adjacent thehole to the inflation lumen to form a hole in the polypropylene tape.

The catheter is tested by inflating and inspecting the anchoringballoon.

TABLE II Tubular Body Tip Outer Coating Shore A Durometer 60$ :5 :5Tensile Strength (p.s.i.) l 100 925 800 Elongation (70) 350 150 700 TearResistance (lbs/in.) 9O 25 100 Type of Silicone Rubber Heat Cured 2 PartRoom I Part Room Temperature Temperature Vulcanizing Vulcanizing Itshould be mentioned that the order of the foregoing steps in the processof producing the catheter of this invention may be varied from thatdescribed without any effect on the catheter. For example, the tip maybe molded to the body before application of the masking tape and theorder of forming holes 26 and 28 may be reversed.

I claim:

1. A method for forming a catheter comprising the steps of:

l. forming a tubular body comprising a primary lumen and an inflationlumen;

2. forming a first hole in said tube to permit communication betweensaid inflation lumen and the exterior of said tube;

3. applying a thin layer of thermoplastic material around the exteriorof said tube to overlap said first 'hole;

4. applying an outer layer of covering material, which does not adhereto the thermoplastic material, to the exterior of said tube to form acovered tube;

5. forming a second hole in the covered tube to permit communicationbetween said primary lumen and the exterior of said covered tube; and

6. forming a third hole in said thermoplastic material adjacent saidfirst hole.

2. The method of claim 1 wherein the step of forming said tubular bodycomprises extruding a silicone tube comprising a primary lumen and aninflation lumen.

3. The method of claim 2 wherein prior to the step of applying saidouter layer of covering material a silicone tip is molded to the distalend of said tube.

4. The method of claim 1 wherein the step of applying an outer layer ofcovering material comprises'dipping said tube in a silicone solution toform an outer layer and drying said outer layer.

5. The method of claim 4 wherein the step of forming said third holecomprises subjecting the outer layerof said catheter to a point adjacentsaid first hole to a heat sufficient to melt a hole in saidthermoplastic material without melting said silicone outer layer.

6. The method of claim 1 wherein the step of applying a thin layer ofthermoplastic material comprises applying a thin layer of thermoplastictape whose adhesive side adheres to said tubular body, whose oppositeside does not adhere to the outer layer of covering material, and whichmelts at a temperature significantly lower than that of said outer layerof covering material.

7. The method of claim 1 wherein the step of applying a thin layer ofthermoplastic material comprises applying a thin layer of unreinforcedtape of a member selected from the group consisting of polyethylene andpolypropylene.

. 8. .The method of claim 1 wherein the step of forming said tubularbody comprises extruding a silicone tube comprising a primary lumen andan inflation lumen and the step of applying an outer layer of coveringmaterial comprises dipping said tube in a silicone solution to form anouter layer and drying said outer layer.

9. The method of claim 6 wherein the step of forming said tubular bodycomprises extruding a silicone tube comprising a primary lumen and aninflation lumen and the step of applying an outer layer of coveringmaterial comprises dipping said tube in a silicone solution to form anouter layer and drying said outer layer.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION PATENT NO. I3,926,705

DATED December 16, 1975 INVENTOR(S) Donald A. Todd It is certified thaterror appears in the above-identified patent and that said LettersPatent are hereby corrected as shown below:

Column 5, line 36, Table I, '1 Part Room**" should read 1 Part Room***Columns 6-7, Claim 1, subparagraphs "l.", "2.", "3.", "4.",

"5.", and "6." should be designated (l) '7 (5) and (6) to distinguishthese subparagraphs of Claim 1 from the remaining claims.

Claim 1, lines 60, 62, 64, and 68 "tube" should be tubular body Signedand Scaled this Twenty-second D ay Of February 1977 [SEAL] Arrest:

RUTH C. MASON C. MARSHALL DANN A! 195N718 ff Commissioner nfParents andTrademarks

1. A METHOD FOR FORMING A CATHETER COMPRISING THE STEPS OF:
 1. FORMING ATUBULAR BODY COMPRISING A PRIMARY LUMEN AND AN INFLATION LUMEN; 2.FORMING A FIRST HOLE IN SAID TUBE TO PERMIT COMMUNICATION BETWEEN SAIDINFLATION LUMEN AND THE EXTERIOR OF SAID TUBE;
 2. forming a first holein said tube to permit communication between said inflation lumen andthe exterior of said tube;
 2. The method of claim 1 wherein the step offorming said tubular body comprises extruding a silicone tube comprisinga primary lumen and an inflation lumen.
 3. The method of claim 2 whereinprior to the step of applying said outer layer of covering material asilicone tip is molded to the distal end of said tube.
 3. applying athin layer of thermoplastic material around the exterior of said tube tooverlap said first hole;
 3. APPLYING A THIN LAYER OF THERMOPLASTICMATERIAL AROUND THE EXTERIOR OF SAID TUBE TO OVERLAP SAID FIRST HOLE; 4.APPLYING AN OUTER LAYER OF COVERING MATERIAL, WHICH DOES NOT ADHERE TOTHE THERMOPLASTIC MATERIAL, TO THE EXTERIOR OF SAID TUBE TO FORM ACOVERED TUBE;
 4. applying an outer layer of covering material, whichdoes not adhere to the thermoplastic material, to the exterior of saidtube to form a covered tube;
 4. The method of claim 1 wherein the stepof applying an outer layer of covering material comprises dipping saidtube in a silicone solution to form an outer layer and drying said outerlayer.
 5. The method of claim 4 wherein the step of forming said thirdhole comprises subjecting the outer layer of said catheter to a pointadjacent said first hole to a heat sufficient to melt a hole in saidthermoplastic material without melting said silicone outer layer. 5.forming a second hole in the covered tube to permit communicationbetween said primary lumen and the exterior of saod covered tube; and 5.FORMING A SECOND HOLE IN THE COVERED TUBE TO PERMIT COMMUNICATIONBETWEEN SAID PRIMARY LUMEN AND THE EXTERIOR OF SAID COVERED TUBE; AND 6.FORMING A THIRD HOLE IN SAID THERMOPLASTIC MATERIAL ADJACENT SAID FIRSTHOLE.
 6. forming a third hole in said thermoplastic material adjacentsaid first hole.
 6. The method of claim 1 wherein the step of applying athin layer of thermoplastic material comprises applying a thin layer ofthermoplastic tape whose adhesive side adheres to said tubular body,whose opposite side does not adhere to the outer layer of coveringmaterial, and which melts at a temperature significantly lower than thatof said outer layer of covering material.
 7. The method of claim 1wherein the step of applying a thin layer of thermoplastic materialcomprises applying a thin layer of unreinforced tape of a memberselected from the group consisting of polyethylene and polypropylene. 8.The method of claim 1 wherein the step of forming said tubular bodycomprises extruding a silicone tube comprising a primary lumen and aninflation lumen and the step of applying an outer layer of coveringmaterial comprises dipping said tube in a silicone solution to form anouter layer and drying said outer layer.
 9. The method of claim 6wherein the step of forming said tubular body comprises extruding asilicone tube comprising a primary lumen and an inflation lumen and thestep of applying an outer layer of covering material comprises dippingsaid tube in a silicone solution to form an outer layer and drying saidouter layer.